1. Field of the Invention
This invention is generally related to the alignment of fabric in sewing machines and more specifically to the automatic alignment of multiple fabric plies prior to stitching in a sewing machine.
2. Description of Related Art
Sewing machines have a wide range of applications, including stitching fabric plies to form a seam. Generally prior art sewing machines include apparatus for feeding fabric plies to a sewing station where a reciprocating needle, thread and bobbin interact to stitch the fabric plies together. In addition, these machines include apparatus for delivering the edges of the fabric plies along a line such that the seam is a fixed distance from the edge and for maintaining the fabric edge along such a line.
The following United States Letters Patent disclose various prior art approaches for feeding and aligning fabric with respect to a sewing station:
U.S. Pat. No. 4,376,415 (1983) Willenbacher PA0 U.S. Pat. No. 4,719,864 (1988) Barrett et al. PA0 U.S. Pat. No. 4,827,858 (1989) Horio et al. PA0 U.S. Pat. No. 4,836,119 (1989) Siraco et al. PA0 U.S. Pat. No. 5,020,460 (1991) Babson et al.
U.S. Pat. No. 4,376,415 to Willenbacher discloses a device for sewing fabric plies together in contour alignment. A cutting mechanism is provided ahead of a sewing or stitching station in a fabric feed direction. A guide unit senses the contour of the fabric edge and controls the cutting mechanism. The fabric plies are secured to each other by spot sealing at some locations whereby a sealing tape is introduced between the plies. This sealing prevents any relative displacement of the plies as they are fed toward the sewing station.
U.S. Pat. No. 4,719,864 to Barrett et al. discloses a limp material seam joining apparatus with a rotatable limp material feed assembly. A selectively operated feeder located coaxially with a needle at a sewing station that reciprocates along a needle axis, transports regions of the material or fabric along a support surface. An orientation controller establishes an angular orientation of the feeder which is selectively rotatable about the needle axis, with respect to the needle. Thus, the offset of the feed axis may be adjusted with respect to a reference axis on the fabric support surface. This apparatus is stated to facilitate the production of curvilinear seams without having to rotate entire sewing machine relative to the fabric or the fabric relative to the sewing machine.
U.S. Pat. No. 4,827,858 to Horio et al. discloses an edge tracing sewing machine having the capability of adjusting needle position automatically. An edge sensor detects the position of a fabric edge in a lateral direction perpendicular to a feed direction. A tracing control device controls a relative position between the needle and the fabric in the lateral direction to form stitches along a line a predetermined distance from the edge. The tracing control device adjusts the relative lateral position between the needle and the fabric edge thereby to maintain a constant offset between the stitching line and the edge.
U.S. Pat. No. 4,836,119 to Siraco et al. discloses a spherical ball positioning apparatus for guiding fabric plies to a sewing station. As a fabric ply slips across a work surface, a drive train, which has one or more drive wheels fictionally engaging a spherical ball, adjusts the fabric feed direction. The drive wheels are preferably located in a spaced, mutually orthogonal relation proximate a great circle on the ball. The relative rotation of the drive wheels causes the spherical ball to rotate and move the fabric in a direction dependent upon the location and orientation of that drive wheel.
U.S. Pat. No. 5,020,460 to Babson et al. discloses apparatus that aligns a fabric ply in a sewing machine using a friction wheel. The friction wheel applies a force to the ply having a component in a direction transverse to the direction of travel. Sensors indicate the lateral position of the edge of the ply. Signals from the sensors and other sources then are combined to control the angular position of the wheel about an axis normal to the fabric ply.
As will be apparent, each of the foregoing U.S. Letters Patent discloses a different approach for directing fabric plies to a sewing station. However, when viewed in their entirety, each approach incurs different operating weaknesses that can be detrimental to the speed or cost of producing a seam. For example, the Willenbacher patent requires spot sealing and the application of sealing tape. The addition of the sealing tape obviously increases the cost of preparing a seam and the complexity of the seaming and feeding operation. The Barrett et al. and Babson et al. patents disclose apparatus in the form of a belt or wheel for changing the feed direction into a sewing station by changing the angular feed direction in the sewing station. Moreover, in each system complex sensor arrays or other inputs taken with the limitation of changing only the angular direction of fabric feed introduce significant time delays between the time the sensors determine a positioning error exists and the time the correction is completed. The Horio et al. provides, as an alternative, the lateral displacement of the needle relative to a feed reference line thereby to increase any error correction. However, this apparatus requires complicated control equipment that adds to the overall cost of preparing a seam. Although the Siraco et al. patent with its driving spherical ball provides two degrees of control, namely, parallel and perpendicular to a feed reference line, the apparatus for maintaining contact and driving the spherical ball can be complicated and expensive thereby adding to the costs of sewing a seam and the reliability of the apparatus.